The human anatomy includes many types of tissues that can either voluntarily or involuntarily, perform certain functions. After disease, injury, or natural defects, certain tissues may no longer operate within general anatomical norms. For example, after disease, injury, time, or combinations thereof, the heart muscle may begin to experience certain failures or deficiencies. Certain failures or deficiencies can be corrected or treated with implantable medical devices (IMDs), such as implantable pacemakers, implantable cardioverter defibrillator (ICD) devices, cardiac resynchronization therapy defibrillator devices, or combinations thereof.
IMDs detect and deliver therapy for a variety of medical conditions in patients. IMDs include implantable pulse generators (IPGs) or implantable cardioverter-defibrillators (ICDs) that deliver electrical stimuli to tissue of a patient. ICDs typically comprise, inter alia, a control module, a capacitor, and a battery that are housed in a hermetically sealed container with a lead extending therefrom. It is generally known that the hermetically sealed container can be implanted in a selected portion of the anatomical structure, such as in a chest or abdominal wall, and the lead can be inserted through various venous portions so that the tip portion can be positioned at the selected position near or in the muscle group. When therapy is required by a patient, the control module signals the battery to charge the capacitor, which in turn discharges electrical stimuli to tissue of a patient via electrodes disposed on the lead, e.g., typically near the distal end of the lead. Typically, a medical electrical lead includes a flexible elongated body with one or more insulated elongated conductors. Each conductor electrically couples a sensing and/or a stimulation electrode of the lead to the control module through a connector module.
In order to deliver stimulation or to perform sensing functions, it is desirable for the distal end of the lead to substantially remain in its position, as originally implanted by a physician. To stay in position, the distal end of the lead can be configured to be actively or passively fixed to tissue of interest. Active fixation refers to a lead electrode placed inside of tissue whereas passive fixation occurs when the electrode is placed on or near the surface of tissue. Actively fixing a lead to tissue can entail twisting a helical coil, disposed at the distal end of the lead, into the tissue of a patient. Suturing the lead to tissue is another active fixation means. While actively fixing the distal end of the lead to tissue substantially ensures that the lead remains in place, the tissue can experience some inflammation. Additionally, in some cases, such as children, active fixation of a lead may be difficult due to the size of the heart. Passive fixation of a lead, developed as an alternative to actively fixing a lead to tissue, involves use of an adhesive on the lead's distal end that can be stuck to the tissue, thereby reducing or eliminating inflammation of the tissue. Cyanocrylate adhesive, disclosed in U.S. Pat. No. 4,282,886, has been used to passively connect a lead to tissue. Alternatively, hydrogel, as disclosed in U.S. Pat. No. 4,768,523, has also been used to passively adhere a lead to tissue. Adhesives are placed directly onto a pad located at the distal end of the lead. The pad is then placed onto the epicardium. These adhesives, placed directly onto the pad, may not be tightly coupled or bonded to the pad. It is desirable to develop implantable medical electrical leads with new adherable fixation mechanisms.